Signaling system



G. DIEDWARDS.

SIGNALING SYSTEM.

APPLICATION FILED NOV-28. 1917.

Patented May 25, 1920.

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unrreo stares PATENT OFFICE.

GEORGE D. nnwanns, or EAST onanen, New JERSEY, Assieivon 'ro wns'riinn' ELECTRIC ooiviranv, INCORPORATED, or new YORK, N. Y., A admonition OF NEW YORK.

SIGNALING SYSTEIII.

Specification of Letters Patent.

Patented May 25, 1926.

Application filed November 28, 1917. Serial No. 204,340.

To all whom it may concern:

Be it known that I, Gnoncn D. EDWARDS, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Signaling Systion of telegraphic impulses from the telephonic circuit so that they are not reproduced by the telephone receivers at the various stations of the system. This object is accomplished by the provision of acomposite circuit having suitable frequency filtering apparatus arranged in the telephonic portion thereof; the filters being designed to prevent passage of currents of low or telegraphic frequencies but to permit the free passage of currents of the relatively higher or telephonic frequencies.

Another object is to provide a composite telephone and telegraph system having an antiside tone telephonic circuit in which currents of telephonic frequencies will be reduced in their effect on the telephonic apparatus by proportioning the relative telephonic transmitting and receiving lllClGI1- cies of such apparatus so that the net telephonic efliciency is substantially maintained while very greatly decreasing the effect of the telegraphic frequencies in such apparatus. To accomplish this purpose, suitable means are provided to increase the transmitting efficiency of the telephonic apparatus relative to'and at the expense of the receiving efficiency so that the decrease in receiving efiiciency which effects reception of both telegraphic and telephonic currents in the telephonic apparatus is practically compensated for by the increased telephonic transmitting efficiency which latter does not, however, affect the telegraphic transmitting efliciency.

Another object of the invention is to provide an anti-side tone telephonic circuit wherein the transmitting efliciency may be readily increased, as desired, and an antiside tone circuit still maintained. To this end telephone sets are provided with suit able means operable to increase the flow of current to the transmitter while at the same time maintaining an anti-side tone circuit through the'transmitter and receiver of the set.

ihe drawing illustrates, in diagrammatic form, one applicationof the invention to a composite system; two stations only being indicated although other stations can be bridged across the line as desired.

The stations, A and B, shown, are each provided with. both telegraphic and telephonic apparatus, the telegraphic apparatus being indicated in the upper rectangles 1 i and 2 respectively, while the telephonic apparatus 1s indicated in the lower rectangles 3 and 4 respectively. A metallic line 5-5 is shown as extending between the various.

stations, but a grounded return may beused if desired.

The telegraphic apparatus shown consists of a telegraphic key 6, a relay 7, and a local sender 8 controlled by the relay Tinthe usual manner. A circuit connection including a condenser 9 extends about the key 6 and relay 7 to provide a pathfor the passage of fluctuating telephonic currents, the 0011-. denser serving to force the telegraphic currents through the windings of relay 7 in the usual manner. The key 6 is shown as open in the drawing, but would ordinarily be closed unless it were being operated in the transmission of telegraphic signals. The windingsof relay 7 are preferably of relatively high impedance while the condenser 9 is preferably of relatively low capacity so that even with the key 6 closed only a small percentage of telephonic currents can pass through the windings ofthe relay 7, while by far the greater percentage will pass freely through the condenser 9. Such telephonic currents as may pass through the windings of the relay 7 will*not operate this relay, due to the relatively low strength of current resulting from telephonic operation of the system. The condenser 9 is preferably made sufficiently low in capacity so that the telegraphic currents will be forced through the relay 7 instead of being shunted around it through the condenser shunt.

Battery for operating the telegraphic portion of the system is arranged between the lines 5 and 5, a battery 10 being shown at each station inthe present case since more satisfactory results are obtained thereby; al-

though a common battery source can be used if desired. A retardation coil 11 is located in the circuit between each of the batteries 10 and the line 5 to regulate the battery supplied to the telegraphic circuit, and to prevent the bridging loss to the telephone circuit which the battery would otherwise cause.

The telephone apparatus shown in the rectangles 3 and 4 is arranged to provide an anti-side tone set and comprises an induction coil 12, the secondary of which is included in a telephonic branch circuit extending between the line wires 5 and 5, and including a condenser 13 of relatively low capacity between the secondary of the coil 12 and the line 5. The coil 12 and condenser 13 are proportioned in such a way that separately and in combination they are inefficient in transmitting the low frequency telegraphic currents impressed upon the line, but highly efiicient in transmitting the relatively higher frequency telephonic currents. In this way the coil 12 and condenser 18 serve to filter out the telegraphic frequencies while efficiently transmitting currents within the usual range of telephonic frequencies.

A transmitter 14. is arranged in a circuit in series with the primary winding of the coil 12, which circuit also includesin series therewith one winding of a second induction coil 15,-the other winding of which furnishes operating current to a telephone receiver 16 arranged in a closed series circuit with the coil winding and a condenser 17. The coil 15, like the coil 12, is also designed to have a low mutual impedance at low frequencies, while the condenser 17' is preferably of relatively low capacity so that the coil 15 and condenser 17 will serve to attenuate and to sensibly extinguish low frequency currents, as hereinafter described.

In order to provide for the maximum efficiency of telephonic systems while at the same time filtering out currents within the usual range of telegraphic frequencies, the coils 12 and 15 are preferably so designed that the mutual impedance. of each of the coilsis low at low frequencies, althoughthe coefficient of coupling is made as .near unity as possible. This arrangement will be best understood from a consideration of the following formulae relating to impedance conditions.

These formulae are 1 z= a? (2) X (wit ne ligib e ca acit )=27T f L (3) X (with apireciable apadity) 1 I 21rfO 4 Zm 46 T X z,

in which Z represents impedance, R, effect1ve resistance, X, reactance, 7, the frequency in complete cycles per second, L, the inductance, U,the capacitance, Zm, the mutual impedance of the transformer, k, the coefficient of coupling between the two windings thereof, and Z and Z the self-impedances of the respective windings of the transformer.

The terms above given are used. in accordance with the meanings outlined in the present standardization rules of the American much as the capacity factor (air) of coil windings, such as used in induction coils for such use, is so small as to be negligible.

Substituting in equation (1) the valuation of X, given in equation (2), gives equation 5 Z /R 211m H b -a e)? which represents the self-impedance of that part of the circuit including a coil winding and a condenser in series therewith.

Applying different numerals to equation '(5) to distinguish the difierent coils of the I transformer, and substituting in equation (4), gives equation which represents the mutual impedance between the two coils of the transformer inclependent of any condenser in series with one of the coils.

v Considering equation, (7 it is evident that if is is made low, the result will be inefficient transformation and transmission at guish currents of frequencies below those which it is desired to have telephonically audible.

Referring to equation (7) it will be seen that either or both the effective resistance, or inductance of either one, or both of the windings can be so proportioned as to make Zm so low as to prevent transmission of currents of telegraphic frequencies through the coils and circuits associated therewith to the receiver 16, while at the same time Zm will be sufficiently high at telephonic frequencies that currents of such frequencies would be efficiently transmitted throughout the telephonic portion of the system. This results from the frequency factor, f, in equa tion 7), inasmuch as the other factors remaining constant the mutual impedance Zm of the coils is a direct function of the frequency of the current passing therethrough.

Any circuit which includes one of the windings of the coil 12 or 15 in series with one of the condensers 13 or 17 respectively has the self-impedance of such part of the circuit represented by equation (6) Inasmuch as the eiiiciency of transmission depends, to a great extent, on the impedance encountered in the circuits and apparatus thereof, it will be apparent that the addition of a condenser in series with one of the windings of coils 12 and 15 is a further element effecting attenuation of currents of low frequency inasmuch as the capacity factor of the condenser in equat on (3) cooperates with the inductance factor (2afL) thereof to produce a marked change in the reactance of the circuit rapidly as the frequency increases or decreases; for example, at a I frequency of 20 cycles per second X would be 1 407TL me while at 900 cycles per second X would be 1 1800A" record In these equations it will also be seen that by using a condenser of relatively low capacity the rate of change in the factor will be more rapid under changes of frequency within the range encountered than where a condenser of relatively greater capacity is used.

From the foregoing it will be apparent that currents of low frequency will be attenuated in passing through that part of the telephone leg of the circuit which in cludes one winding of the coil 12 in series with the condenser 13, while further attenuation is accomplished, due to the low mutual impedance ofthe coil 12, at low frequencies. Any part of such low frequency currents which are not extinguished by the condenser 13 and coil 12 would flow through the primary winding of the coil 15 which, having a low mutual impedance. at low frequencies, would still further extinguish currents of such low frequencies. The condenser 17 in series with the secondary winding of the coil 15 would also increase the low frequency impedance of the receiver circuit so as to practically extinguish such low frequency currents as might pass the coil 15 or to reduce them to such a low strength that the receiver 16 would not function to translate such currents into audible sounds.

The reactance of the condenser 17 in the receiver circuit at talking frequencies may be practically annulled by that of the receiver 16 and of the receiver induction coil 15; the receiver 16 preferably being of relatively high impedance. Telegraphic frequencies as used in this case is intended to apply to frequencies generated in the course of ordinary key transmission together with the lower harmonics of such frequencies which would ordinarily not exceed 100' cycles per second; while telephonic fre-- quencies as here used is intended to apply to frequencies beginning as low as 200 cycles per second and running up to the limit of audibility.

Referring now to the transmitter circuit, the transmitter 14 is included in a local battery circuit. This circuit leads from one side of a local battery 18 through the transmitter 14, conductor 19, thence normally by conductors 20 and 21 through a non-inductive balancing resistance 22 and conductor 23 to an intermediate point of the primary winding of the coil 12 and through the lower portion of this winding to the other side of the battery 18. A parallel circuit is also normally provided beginning at conductor 21 and extending through a manually operated key 24 and the normal contact thereof, conductors 25 and 26, primary winding of coil 15, conductor 27, and upper portion of the primary winding of coil 12 to conductor 23. A second noninductive resistance 28 of relatively greater value than resistance 22 is connected between conductors 20 and 26 but is normally shunted out by the low resistance path from conductor 19 through conductor 20, key in engage ment with its normal contact, and conductor 25 to conductor 26. Ihis arrangement furnishes a circuit which is advantageous in preventing a speaker hearing his own voice too strongly, and also serves to prevent cu-r rents set up in a transmitter by extraneous sufiicient strength to set up audible side tones in the receiver. This result is due to the fact that the current variations produced by the local transmitter l l flowing through the lower portion of the primary of the induction coilv 12 induced currents of counter-electromotive force in the upper portion of the primary of the coil 12 of such value and direction as to practically neutralize the currents which would otherwise flow through the local receiver induction coil 15; through the parallel circuit normally existing about the resistance 22 in the transmitter circuit previously traced. Under these conditions practically no transmitting current flows through the primary of the receiver induction coil 15 during transmission at that station. It will be noted that a greater number of turns of the primary of the coil 12 are included in the local transmitting circuit than in the local receiving circuit. The purpose of this arrangement is to obtain an increased telephonic transmitting efliciency and a somewhat less relative receiving eiiiciency while still preserving the anti-side tone features of the set. The decreased receiving efliciency serves to reduce the strength-of both telegraphic and telephonic currentsreceived at the primary of the receiver induction coil 15. This reduction in the case of telephonic currents is offset by the increased telephonic transmitting eiliciency but does not increase the telegraphic currents, and thus elfects a reduction of the telegraphic currents received in the telephonic circuit without reducing the net telephonic efliciency over a set having identical transmitting and receiving efliciencies.

When telephonic communication is being carried on under noisy conditions at either the transmitting or receiver stations, it is desirable that the parties talking be provided with means whereby they can temporarily increase the transmitting efiiciency of their respective telephone sets. To accomplish this result, and at the same time preserve the anti-side tone feature of the circuit, the circuit is so arranged that by engaging the key 2% with its. alternate contact the resistance 22 is short-circuited by the conductor 29 and the resistance 28 connected in series with the primary 01": the coil 15. The shunting out of resistance 22 lowers the resistance of the transmitter circuit and increases the currents supplied by the battery 18 to the transmitter 1 1 and at the same time prevents any appreciable current from the battery 18 reaching the coil 15. The resistances 22 and 28, together with the other apparatus in the circuits, are so proportionedthat while the receiving efficiency is decreased and the transmitting efficiency increased under these conditions, the receiving efliciency will still be great enough so that any answers or interruptions made by the party at the receiving station will be clearly audible atthe receiver 16 of the transmitting station.

During telephonic connection, fluctuating voice currents originate at one station, and

passing through the primary of the coil 12 at that station, induce corresponding currents in the secondary of the coil 12 thereat. These induced currents being of telephonic frequency will pass freely through the condenser 13 to the. conductor 30 and through the condenser 9 ofthe telegraph set at the transmitting station, over the line 5; through the condenser 9 of the telegraph set, conductor 30, condenser 13 and secondary of the coil at the receiving station, to the return line 5 leading to the lower side of the sec-- ondary of the coil 12 at the transmitting station. Telephonic currents passing through the secondary of the coil 12 at the receiving station induce corresponding currents in the primary thereof. The currents induced in the upper portion of the primary of this coil flow through the primary of the receiver induction coil and normally through the balancing resistance 22 to the junction of the upper and lower portions of the primary winding of the coil 12. When the key 24 is operated to engage the conductor 29, the balancing resistance 22 is shunted out, while the higher resistance 28 is connected in series with the primary of the coil 15,

thereby diminishing the strength of current I flowing therethrough to reduce the receiving etiiciency, but at the same time increasing the transmittingefficiency of that station, as previously described.

lfn practice, the key 24 at a station is operated only when the called party thereat desires to. temporarily increase the transmitting efiiciency while actually talking to another party, and this key would normally be released when the party called was replying, although the receiving efiiciency at the original transmitting station is sufficient so that the party thereat can understand interruptions from other stations even though his key 24- be depressed. On releasing the key, the receiving efi'iciency is increased to'its normal condition, while the transmitting efiioiency is at the same time diminished to itsnormal value, which, however, is sufiicient to operate satisfactorily under normal transmitting conditions. I c

lVhat is claimed is:

1. In an electrical signaling system, a telephonic receiver, a telephonic transmitter, a transformer having a plurality of windings inductively associated, a source of direct current, a circuit including the transmitter and source of current in: series with a portion of one of the transformer windings, a

1 second circuit in parallel with the first circuit including the source of current and another portion of the transformer winding included in the, first circuit, a telephone re- .ceiver operatively associated with the parallel circuit, and a third circuit including another of the transformer windings.

2. In a combined telephone and telegraph system, a telephonic receiver, a plurality of condensers, two transformers each having a plurality of windings inductively associated, a circuit including one winding of one of said transformers arranged in series with one of said condensers and with said receiver, another winding of such transformer being arranged in series with one winding of the other transformer, and a second circuit including another winding of such other transformer arranged in series with another of said condensers; the impedances of said windings and the capacitances of said condensersbeing so proportioned that the combined mutual impedances of said transformers and condensers are low at telegraphic frequencies and relatively higher at telephonic frequencies, while the self-impedances of said circuits are relatively high at low frequencies and relatively low at high frequencies, whereby currents of telegraphic frequencies are practically extinguished before reaching said telephonic receiver, while currents of telephonic frequencies are transmitted to said receiver with but relatively slight attenuation or sensible extinguishment.

3. In a telephone system, a transmitter, a transformer having a plurality of windings inductively associated, a source of current, a IGSlStflJlCB, a c1rcu1t normally including said transmitter, the source of current and resistance in series with a portion of one of said transformer windings; a shunt circuit about a portion of said first circuit and in cluding another portion of the transformer winding included in said first circuit, a telephone receiver operatively associated with said shunt circuit, and means to effectively remove said resistance from said first circuit to change the strength of current supplied to said transmitter. I

4. In a telephone system, a transmitter, a transformer having a plurality of windings inductively associated, a source of current, a resistance, a circuit normally including said transmitter, the source of current and resistance in series with a portion of one of said'transformer windings; a shunt circuit aboutia portion of said first circuit and including another portion of the transformer winding included in said first circuit, a telephone receiver operatively associated with said shunt circuit, and means to effectively remove said resistance from said first circuit to increase the strength of current supplied to said transmitter.

5. In a telephone system, a transmitter, a transformer having a plurality of windings inductively associated, a source of current, a resistance, a circuit normally including said transmitter, source of current and resistance in series with a portion of one of said transformer windings; a shunt circuit about a portion of said first circuit and including another portion of the transformer winding included in said first circuit, a telephone receiver operatively associated with said shunt circuit, means to efiectively remove said resistance from said first circuit to change the strength of current supplied to said transmitter, and means to maintain said shunt circuit on effective removal of said resistance from said first circuit.

6. In a telephone system, a transmitter, a transformer having a plurality of windings inductively associated, a source of current, a resistance, a circuit normally including said transmitter, source of current and resistance in series with a portion of one of said transformer windings; a shunt circuit about a portion of said first circuit and including another portion of the transformer winding included in said first circuit, a receiver operatively associated with said shunt circuit, a second resistance, means to effectively remove said first resistance from said first circuit, and means to effectively include said second resistance in said shunt circuit on the effective removal of said first resistance from said first circuit.

7. In a telephone system, a transmitter, a transformer having a plurality of windings inductively associated, a source of current, a first resistance, a circuit normally including said transmitter, source of current and resistance in series with a portion of one of said transformer windings, a shunt circuit about a portion of said first circuit and including another portion of the transformer winding included in said first circuit, a receiver operatively associated with said shunt circuit, a second resistance of greater value than said first resistance, means to effectively remove said first resistance from said first circuit, and means to eifectively include said second resistance 1n said shunt circuit on the effective removal of said first resistance from said first circuit.

8. In a combined telephone and telegraph system a plurality of telephonic stations, telephonic transmitting and receiving apparatus at each of said telephonic stations, a plurality of telegraphic stations, telegraphic transmitting and receiving apparatus at each of said telegraphic stations,'a common conductor to carry both telegraphic and telephonic currents between said stations, said telephonic apparatus comprising a transmitter, a receiver, an anti side-tone circuit including sa d transmitter and receiver, and meansmcluded in said c1rcu1t increasing the transmitting efficiency and decreasing the relative receiving efficiency of the circuit; whereby both telephonic and telegraphic currents received at a receiving station are diminished, while the increased efficiency of telephonic transmission substantially compensates for the decreased telephonic receiving efiiciency without affecting the telegraphic transmitting efliciency.

9. In a combined telephone and telegraph system, a plurality of telephonic stations, telephonic transmitting and receiving apparatus at each of saidtelephonic stations, a plurality of telegraphic stations, telegraphic transmitting and receiving apparatus at each of said telegraphic stations, a common conductor to carry bothtelephonic and telegraphic currents between said stations, said telephonic apparatus comprising a transmitter, a receiver, a transmitting circuit, a receiving circuit, said circuits being associated to provide an anti side-tone circuit, and a transformer having a plurality of windings, one of said windings being connected with said conductor and another of said windings having different portions thereof included respectively in said transmitting and receiving circuits, the proportions of said winding included in the respective transmitting and receiving circuits being such that the transmitting efficiency of said transmitting circuit is increased relative to the receiving efficiency of said receiver circuit; whereby both telephonic and telegraphic currents received in said telephonic receiving circuit are of diminished magnitude while the increased efficiency of said transmitting circuit substantially compensates for the'decreased telephonic receiving efficiency of said receiving circuit without affecting the telegraphic transmitting efficiency.

10. In a telephone system, a transmitter, a source of dlrect current, a circuit includ- 1ng sald transmitter and source of current,

a second circuit in parallel withthe first circuit including said source of current, a telephone receiver operatively associated with said second circuit, and means independent of the transmitter to change the relative resistance of said first and second circuits to increase the strength of current supplied from said source of current to said transmitter and to decrease the strength of current supplied from said source of current to said second circuit during the operative association of said transmitter and receiver.

11. In a telephone system, a transmitter, a source of direct current, a first circuit including the transmitter and source of current, a receiver, with the first circuit including the transmitter and'source of current and operatively associating the receiver with the transmitter, and means independent ofthe tr ansmitter'to increase the relative strength of current sup a second circuit in parallel plied to one of these circuits from the source of current during the operative association of the transmitter and receiver when the relative strength of current suppliedto the other of these circuits is decreased.

12. In a telephone system, a transmitter,

a source of direct current, a first circuit in cluding the transmltter and source of current, a recelver, a second (3113011113 ncluding the transmitter and source of current operatively associating the receiver with the transmitter, and means independent of the transmitter to decrease the relative strength of current supplied to the second circuit from the source of current when the relative strength of current supplied to the first circuit from the source of current is increased during the operative association of the transmitter and receiver.

taneously decrease the relative strength of current from the source supplied to the second'circuit when this means is operated to increase the relative strength of current from the source supplied to the first circuit during the operative association of the transmitter and receiver.

14:. In a telephone system, a transmitter, a source of direct current, a first circuit including the transmitter and source of current, a receiver, a second circuit including the transmitter and source of current operatively associating the receiver with the transmitter, means associated with the two circuits regulating the normal division of current from the source of current between the two circuits during the operative association of the transmitter and the receiver, and means to change the association of the regulating means with the two circuits to simultaneously increase the relative strength of current in one of the circuits and to decrease the relative strength of current in the other of the circuits. 7

15. In a telephone system, a transmitter, a source of direct current, a resistance, a first circuit including the transmitter, source of current and resistance therein, a receiver, a second circuit in parallel withthe first circuit including the source of currenttherein operatively associating the receiver With the transmitter,.and means operable during the operative association of the receiver and transmitter to effectively remove the resistance from the first circuit while preserving the continuity of both of the circuits to increase the rela .cuits to increase cluding the source of-current therein and operatively associating the receiver with the transmitter, and means operable during the operative assoclation of the receiver and transmitter to efiectively remove the first resistance from the first circuit and to effectively include the second resistance in an individual portion of the second circuit while preserving the continuity of both cirfrom the source of current in the first circuit and to decrease the strength of current in the second circuit.

17 In a telephone system, a transmitter, a source of direct current, a transformer having a plurality of windings, a first circuit including the transmitter, source of current and a portion of one of the windings, a telephone receiver, a second circuit in parallel with the first circuit including the source of current and another portion of said one of the windings and operatively associating the receiver with the transmitter, and means to inversely vary the relative strength of current supplied from the source of current to therespective portions of said one of the windings included in the respective circuits during the operative association of the transmitter and receiver.

18. In a telephone system, a transmitter the strength of currentv member, a source of direct current, a transformer having a plurality of windings, a circuit including the transmitter member, source of current and a portion of one of the windings therein, a telephonic receiver member, a second circuit in parallel with the first circuit including the source of current and another portion of said one of the windings and operatively associating the receiver member with the transmitter member, and means to inversely vary therelative strength of current from the source of current to the members through their respective portions of said one of the windings during the operative association of the members.

19. In a telephone system, a transmitter, a source of direct current, a transformer having a plurality of windings, a circuit including the transmitter, source of current and a portion of one of the windings therein, a receiver, a second circuit in parallel with the first circuit including the source of current and another portion of said one of the windings and operatively associating the receiver with the transmitter, simultaneously increase the relative strength of current from the source of current supplied to the transmitter through the portion of the winding included in the first circuit and to decrease the relative strength of ourand means to rent supplied to the receiver through the I portion of the winding included in the second circuit during operative association of the transmitter and receiver.

In witness whereof, I hereunto subscribe my name this 26th day of November, A. D., 1917.

GEORGE D. EDWARDS. 

